Galvalume Re-roof

We want to replace an existing asphalt shingle roof (12 years old) with a metal roof. We've contacted several contractors, received estimates and now have to make a decision as to which system to install.
We have some questions which we need answered before we decide. Because of the significant difference in price, we are wary that one or the other is offerring a lower quality/perfoming installation.
We do not want you to comment on pricing. However, it would be extremely helpful if you could address our specific concerns.
1] Is a multilayered installation,(eg. 30lb felt paper, over existing shingles, 5/8"@ layer of polyisocyanate, topped by 29 gauge, pre-painted galvalume panels attached to a system of metal purlins and the plywood substrate) superior to a high-reflective, foil radiant barrier, over existing shingles, topped with 29 gauge, pre-painted galvalume panels attached directly to the plywood substarate? Or is it the first over-engineered?
Both installations will use stainless steel screws to secure the roofing to the plywood substrate.
2] Can you supply a list of manufacturers that produce a pre-painted, galvalume steel product with a warranty that does not exclude installations near (less than 1000 meters) from the ocean?
Thank you, tourettica

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I think you need to back up a little and look at a few things such as ventilation and location. If you have a vented attic construction none of your proposed assemblies does much for reducing energy.I am assuming that you have a vaulted ceiling and are located in a Southern climate.
The IBC and IRC building codes call for a minimun of 1" vented free air space under the roof covering. While this is more important in the cold in winter climates, the warm climates still generate condensation and it needs to be vented. As well it will stop heat transfer.
Uncoated Galvalume has excellant weathering and reflective properties but is low emittance properties. First in the ocean environment I would use an AZ55 coated Galvalume for extra durablity against salt air and you may want to consider a white PVDF paint on it which increases the emittance significantly.
The reflective foil barriers work best when located approximately 1" under the roof covering which fits in well with the ventilation required.
If you are having concerns about wind issues, I would suggest removing the existing shingles and start fresh to ensure you get a proper attachment. If you need an insulation upgrade then add a proper amount of ridgid over the decking, then a porper underlay moisture barrier, vertical strapping over and fastened to the rafters and then horizontal strapping and then an energy star metal roof that is vented at the eaves and ridge.
As to product manufacturers please go to our member manufacturers and contact the ones producing your profile and contact them in regards to warranty and always ask to see the product approval report which dictates how to install it correctly.

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Dear Mr. Reid:
Thank you for your prompt response. The home in question is located on the east coast of Florida, 40 miles north of Daytona Beach, and 800 to a 1000 ft from the ocean.
The home is a 2 story wood frame dwelling with an asphalt shingle roof. The roof is vented by continuous aluminum soffits and two ridge vents. A small portion of the interior ceiling is vaulted (@ 125sq.ft.). The overall area between the interior ceilings and the underside of the plywood roofing substrate is, on average, significantly more than 1 inch.
With this in mind would you please comment further on the efficacy and efficiency (both as to appearance & utility) of the installations mentioned in my original e-mail.
Thank you,
tourettica

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Your goal is to keep your home cooler, reduce energy cost and make it more comfortable. Reflective underlay gets its benefits from reflecting rays of heat. We have had some excellant results using it in retrofit of church roofs where there is no insulation and they ca'nt afford a complete upgrade. In this type of installation where there is 1" of space, it helps reflect out heat rays in the summer and reflects heat rays back in in the winter. This does nothing to stop heat loss frm air leakage.
In yoyur case the most benefit is to reflect out the heat from the sun to reduce AC costs. If this is all you did then it works and again works best with a 1" air space separating it from the roof covering. Insulation is a much more effective method to keep out the heat however it does generally cost more. On that point I would give it to the ridgid insulation quote. One must remember though that you are in a high wind area and the manufacturer will have certain requirements for installation to hold the roof on which may have a bearing. Currently I do not know of any 29 ga material that has met the HVHZ requirement in the new FL code. That product is fine on minimum 5/8" plywood decking applied with a proper size and amount of screws directly over or it requires a close spacing on the strapping.
I would be choosing an energy star rated product that has high emissivity properties and one that is designed to stand off the deck so heat does not transfer. This will do more that either the 1" insulation or the reflective barrier. Add either underneath and the system gets better.

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Dear Mr.Reid:
By the "rigid installation quote" do you mean the multilayered, purlin mounted install or the other? Will condensation be a problem with the continuous aluminum soffets or will they actually help keep the roof more viable?
Thank you,
tourettica

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One type of rigid insulation is polyisocyanate which is designed to take higher heats than syrofoam however the insulation values are typically lower per inch.
As to the ventilation. This needs to be calculated. Get the "net free area" for the soffitt material from the manufacturer, also make sure that it is not blocked underneath and has free access up into the attic. Take the flat ceiling area and devide by 150 and you are required to provide this amount of free area each at the eaves and ridge balanced.
Proper ventilation is the most imortant item in the roof assembly to keep it and your home healthy.

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